The present application claims priority under 35 U.S.C. xc2xa7 119 of German Patent Application No. 199 14 709.4, filed on Mar. 31, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to a process for producing a resilient roll having a hard roll core. In particular, the roll core can be of metal and is provided with a resilient covering layer. In order to form the covering layer, an inner connecting layer is applied to the roll core and an outer functional layer is applied to the connecting layer. Further, in order to form the connecting layer, a fiber bundle including a large number of fibers is wound onto the roll core, the winding direction of the fibers running essentially parallel to one another and at an angle to the circumferential direction of the roll core.
Furthermore, the present invention is directed towards a roll, in particular for smoothing paper webs, having a hard roll core, which can be of metal, and which is provided, on its outer side, with a resilient covering layer. The resilient covering layer comprises an outer functional layer and an inner connecting layer for connecting the functional layer to the roll core. The inner connecting layer comprises a matrix material with fiber layers which are embedded therein and which are positioned radially one above another.
2. Discussion of Background Information
Resilient rolls of this type are used, for example, in the calendering of paper webs. An elastic roll and a hard roll form a press nip, through which the paper web to be processed is directed. While the hard roll has a very smooth surface, consisting, for example, of steel or hard cast iron and is responsible for smoothing that side of the paper web which faces it, the resilient roll acting on the opposite side of the paper web serves to compact and make uniform the thickness of the paper web in the press nip. The resilience of this second (i.e., resilient) roll therefore prevents a too intensive compacting of the paper web, which would lead to a specky appearance of the paper web. The rolls are on the order of from about 6 to 12 m long and of from about 800 to 1500 mm in diameter. The rolls withstand line forces of up to approximately 600 N/mm and compressive stresses of up to approximately 50 N/mm2.
Since the trend in paper manufacture is for calendering to be carried out on-line, (i.e., the paper web leaving the papermaking machine or coating machine is immediately led through the paper smoothing device or calendering device), higher requirements than previously are placed on the rolls of the smoothing device, particularly with respect to their temperature resistance. The high transport speeds of the paper web, necessitated by on-line operation, and the associated high rotational speeds of the calender rolls, increase their alternating flexure frequency, which in turn leads to increased roll temperatures. These high temperatures, produced in on-line operation, lead to problems which, in the case of known resilient rolls, can lead to the destruction of the synthetic covering of the roll. On one hand, in the case of known synthetic coverings, maximum temperature differences of about 20xc2x0 C. over the width of the roll are permissible and, on the other hand, the polymers normally used for the coating have a significantly higher coefficient of thermal expansion than the steel rolls or hard cast iron rolls normally used for the core roll. Accordingly, as a result of an increase in the temperature, high axial stresses occur between the steel or hard cast iron core roll and the synthetic coating connected to it.
As a result of these high stresses, associated with heated locations occurring at certain points or regions within the synthetic coating, so-called hot spots can occur, as a result of which the separation or even the bursting of the synthetic layer takes place.
These hot spots tend to occur in particular when, in addition to the mechanical stresses and the relatively high temperatures, there are crystallization points in the form of, for example, faulty adhesive bonds, deposits or above average bulges in the resilient covering. Such bulges can occur, for example, as a result of creases or foreign objects on the paper web. In such cases, the temperature at these crystallization points can rise from a normal of about 80xc2x0 C. to 90xc2x0 C. to more than 150xc2x0 C., which results in the aforementioned deterioration of the synthetic layer.
The present invention relates to a process for producing a resilient roll having a hard roll core and a resilient covering layer. The roll is formed by applying a radially inner connecting layer to the roll core and applying a radially outer functional layer onto the connecting layer. The connecting layer is formed by winding a fiber bundle comprising a plurality of fibers onto the roll core. The winding direction of the fibers is substantially parallel to one another and at an angle to the circumferential direction of the roll core. Thus, a plurality of fiber layers are wound over one another and the angular orientation of successive fiber layers with respect to the longitudinal axis of the roll core is different.
Further, the fiber bundle of two immediately successive fiber layers are wound in opposite directions such that angular orientations of the two immediately successive fiber layers are symmetrical with respect to the cross-sectional area of the roll. The angle with respect to the longitudinal axis of the roll of the fiber bundles for the individual fiber layers increases radially outwards from the center of the roll. The angle, with respect to the longitudinal axis of the roll of inner layers of fiber bundles is about 30xc2x0 to 40xc2x0. Further, the angle, with respect to the longitudinal axis of the roll, of successive fiber layers increases in steps of about 10xc2x0 to 200xc2x0.
According to a further feature of the present invention, the fiber bundles are formed by fiber rovings, a roving comprising a plurality of fibers of identical type positioned beside one another. Further, the fibers are at least one of glass fibers and carbon fibers. In forming at least one of the connecting layer and the functional layer, glass fibers and carbon fibers are wound simultaneously onto the roll core.
Further, during the winding, a large number of glass fiber and carbon fiber rovings positioned to about one another are simultaneously wound onto the roll core to form a roving layer. Before being wound onto the roll core, the glass fibers and carbon fibers are surrounded with a matrix material.
The hard roll core can be comprises a metal roll core.
Further, the angle, with respect to the longitudinal axis of the roll, of successive fiber layers can increase in steps of about 15xc2x0.
In addition, in forming at least one of the connecting layer and the functional layer, glass fibers and carbon fibers are wound simultaneously onto the roll core. Further, the matrix material comprises a resin/hardener combination.
The glass fibers and carbon fibers are drawn through a resin/hardener bath. The glass fibers and the carbon fibers can be simultaneously wound dry onto the roll core and have a matrix material applied to them after the winding operation. In addition, the glass fibers and the carbon fibers can be completely embedded in the matrix material.
The matrix material can be a polymer which can be one of a thermosetting polymer and a thermoplastic polymer.
The mixture ratio of glass fibers to carbon fibers can be between about 60/40 and about 90/10. Further, the mixture ratio of glass fibers to carbon fibers is about 70/30.
The fiber content of the connecting layer c(an be between 50 and 60% by volume. Further, the fiber content of the connecting layer can be about 55% by volume. In addition, the fiber content of the functional layer can be between about 8 and 12% by volume.
Further, the fiber content of the connecting layer can be between about 40 and 70% by volume. In addition, the fiber content of the functional layer can be between about 5 and 20% by volume.
The present invention also relates to a roll, adapted for use in smoothing paper webs, which has a hard roll core and a resilient covering layer. The covering layer can be an outer functional layer and an inner connecting layer that connects the functional layer to the roll core. The inner connecting layer includes matrix material with embedded fiber layers, the fiber layers being positioned radially one over the another. The fiber layers each comprise fibers wound at a predetermined angle to the longitudinal axis of the roll core and extending essentially parallel to one another. For different fiber layers, the predetermined angle of the fiber layers with respect to the longitudinal axis of the roll core is different.
The predetermined angle of the fiber layer increases as distance from the roll core increases. Further, the matrix material can be a polymer. Further, the matrix material comprises a resin/hardener combination.
The fiber bundles of two immediately successive fiber layers extend in opposite directions such that orientations of the fiber bundles of two immediately successive fiber layers are symmetrical with respect to the cross-sectional area of the roll.
The predetermined angle, with respect to the longitudinal axis of the roll of the individual fiber layers increases radially outwardly. Further, the predetermined angle in the inner fiber layers is between about 30xc2x0 and 40xc2x0. In addition, the predetermined angle can increase in steps of about 10xc2x0 to 20xc2x0.
According to a further feature, the fiber bundles comprise fiber rovings, a roving comprising a number of fibers of identical type lying beside one another. The fibers are at least one of glass and carbon fibers. At least one of the inner connecting layer and the outer functional layer is made up of a mixture of glass fibers and carbon fibers, which are embedded in a matrix material and are distributed essentially uniformly over the length of the roll.